Fever of unknown origin and Q-fever: a case series in a Bulgarian hospital

Background: Fever of unknown origin (FUO) is a perplexing medical problem. The causes for FUO are more than 200 diseases. The aim of the study was to present human clinical cases of Coxiella burnetii infection debuting as FUO. Methods: The following methods were conducted in the study: literature search, laboratory, imaging, and statistical methods. Criteria of Durack and Street were applied for FUO definition. For the etiological diagnosis indirect immunoenzyme assay (ELISA) for antibodies detection against Coxiella burnetii was used (cut-off = 0.481–0.519). Results: From 2008 until 2015, nine patients with FUO caused by C. burnetii were hospitalized at the Military Medical Academy of Sofia. Male gender was predominant (male/female – 77.8% /22.2%), mean age was 48.78±14.52 years (range: 26–67), hospital stay was 9.78±2.95 days (range: 5–15), fever duration was 54.33±56.23 days (range: 21–180). Laboratory investigations estimated the elevation of erythrocyte sedimentation rate 49.11±31.74mm/h (95%CI = 13.09–111.31), C-reactive protein 37.68±37.62mg/L (95% CI = 36.07–111.42) and fibrinogen 5.69±1.59g/L (95% CI=2.57–8.81). The mean values of liver enzymes were in reference range. Among imaging tests, abdominal ultrasound and X-ray demonstrated 33.3% contribution to the final diagnosis. Transthoracic echocardiography found 22.2% contribution. Serological methods presented 100% contribution. Conclusion: C. burnetii infection was accepted as a final diagnosis among 9 patients with FUO based on the integrated information from the applied methods. Active search and establishment of this pathogen among FUO should lead to avoiding potential complications and consequences in case of untreated patients infected with C. burnetii.

F or the first time, fever of unknown origin (FUO) was defined in 1961 by Robert G.
Petersdorf and Paul B. Beeson (1). They gave the following definition of FUO: (a) fever higher than 38.3 0 С (101 0 F) in several measurements; (b) duration of fever for at least 3 weeks; (c) diagnosis remains unclear after a week of active diagnosis in a hospital (1). In 1991 two other American researchers David T. Durack and Alan C. Street changed the third criterion for FUO in the following form: "the diagnosis remains unspecified after 3 outpatient visits or 3 days in hospital" (2). Dutch scientist Chantal P. Bleeker-Rovers has presented a new definition of FUO in 2007 (3). Professor Bleeker-Rovers retained the first two criteria and removed the third criterion (3,4). The researcher added a new third criterionexclusion of immunocompromised individuals and a fourth criterion for a mandatory diagnostic investigation (3,4).

Methods
Study design and participants: An observational study was conducted between January 2008 and March 2015 at the Department of Infectious Diseases, Military Medical Academy, Sofia (Bulgaria). The definition of Durack and Street for FUO was applied in the present study (2). Patients older than 18 years were enrolled (2). Measurements of body temperature were performed with a digital thermometer MC-343F-E (OMRON Flex Temp Smart; OMRON Healthcare Co., Ltd., Ukyo-ku, Kyoto, Japan), accuracy of measurement ±0.1 0 С (range: 32.0 0 С-42.0 0 С). The thermometry was realized in the axillary area under the supervision and control of a physician or nurse at an ambient temperature of 20.0 0 C to 28.0 0 C. Laboratory and diagnostic tests: Various laboratory tests have been applied during the diagnostic process: WBC, ESR, Fibrinogen, CRP, AST, ALT, GGT, AP and other laboratory indicators. Depending on the medical history and physical examination and diver imaging studies were carried out: abdominal ultrasound, x-ray, transthoracic echocardiography, computed tomography. Etiological diagnosis included culture methods, serology tests and molecular assays. Coxiella burnetii phase 1 IgA/IgG and Coxiella burnetii phase 2 IgG/IgM antibodies were detected in serum by indirect immunoenzyme assay (SERION ELISA classic, Virion/Serion, Würzburg, Germany), and according to the manufacturer's instructions. Coxiella burnetii phase 1 IgA/IgG sensitivity 94.2%, specificity 96.2%; C. burnetii phase 2 IgG sensitivity 93.4%, specificity 98.5%; and C. burnetii phase 2 IgM sensitivity 94.4%, specificity >99%. The cutoff-evaluation of C. burnetii phase 1 IgA and IgG, respectively C. burnetii phase 2 IgM were calculated for each sample according to the manufacturer's prescription and varying between from 0.481 to 0.519. Coxiella burnetii phase 1 IgA/IgG, resp. C. burnetii phase 2 IgM were defined as positive when optical density (OD) sample is more than 10% over OD cutoff, as negative when OD sample is more than 10% under OD cutoff, and as borderline when OD sample +/-10% of OD cut-off. SERION ELISA classic C. burnetii phase 2 IgG was expressed in U/ml titer using a mathematical calculation and was defined as positive when the titer was >30 U/ml, as negative when the titer was <20 U/ml, and as borderline when the titer was 20-30 U/ml.

Results
In the period of January 2008 to March 2015, one hundred and thirteen patients with FUO were investigated at the Department of Infectious Diseases, Military Medical Academy, Sofia (Bulgaria). The distribution of etiological groups was: 58.4% infections, 4.4% neoplasms, 13.3% noninfectious inflammatory diseases, 5.3% miscellaneous and 18.6% undiagnosed cases.
After a comprehensive diagnostic process nine patients were classified as C. burnetii infection. They had serological data for Q-fever. The final diagnosis was determined by medical history, laboratory data and positive serological results.
Divers reasons could influence this result. First, the geographic location of Bulgaria and local climate create a good condition for the development of this infection. Second, the hygiene requirements of livestock farms (cows, sheep, goats) are very often lowered. Third, veterinary control of dairy products (milk, cheese, yellow cheese, butter) is not always enough protective in the rural area of Bulgaria. Fourth, weather conditions for the development of ticks (as vectors for transmission of C. burnetii) are appropriate in our country.
In the present study, the mechanism of infection is unclear, the epidemiological data are not enough to summarize the potential way of transmission. All this require further researches in the field of Q-fever and FUO in Bulgaria.
In conclusion, the diagnostic detection of any case of FUO is a serious challenge for the physician. Q-fever as a cause of FUO is a reason, requiring a high attention in the diagnostic process.
The scientific data for the connection between Q-fever and FUO are small. All these facts are a start point for further investigations.